JP4352502B2 - Acidity measuring device and acidity measuring method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a measuring instrument that has a working electrode and a counter electrode and a comparison electrode or a working electrode and a counter electrode, and that electrochemically measures a sample, and is mainly a free fatty acid contained in edible oil and an apple contained in a fruit drink The present invention relates to an acidity measuring device and an acidity measuring method for measuring the acidity of acids, tartaric acid, acids contained in alcoholic beverages, or coffee acids in coffee.
[0002]
[Prior art]
In recent years, by investigating the components in a substance, the characteristics of the substance have been grasped and have been used for various developments. For example, the amount of dissolved oxygen and the amount of chemical oxygen supplied in water indicate the amount of water contamination, and the amounts of nitric acid, various metals and organic substances in the soil also indicate the amount of soil contamination. Among them, foods are required to have a certain level of quality from the viewpoint of health and safety, and among them, acids contained in foods greatly affect the quality of foods. This acid will be explained in detail. Food acidity includes edible oil, fruit drinks such as juice, alcoholic drinks such as whiskey, liquor, wine, coffee, etc. Was using the law.
[0003]
There are various methods for measuring this neutralization. For example, the standard oil analysis method, Japan Agricultural Standards, JIS, Japanese Pharmacopoeia oil test method, hygiene test method food test method, water test method, etc. Although there are defined methods, the basis of the measurement of all is phenolphthalein as an indicator. A detailed description of this neutralization titration method is well known to those skilled in the art, and is therefore omitted.
[0004]
By the way, as a method for measuring the acid, there is a method of measuring the acidity by voltammetry regardless of the neutralization titration method. This is disclosed in Japanese Patent Application Laid-Open No. 5-264503, in which a coexisting electrolytic solution in which a free fatty acid and a naphthoquinone derivative coexist is measured by voltammetry using a potential regulating method. The magnitude of the pre-reduction wave current value of the naphthoquinone derivative is proportional to the free fatty acid concentration for all fatty acids from lower fatty acids such as formic acid to higher fatty acids such as oleic acid and linoleic acid, and the current value of each fatty acid. Is utilized that corresponds to the total concentration of fatty acids. That is, the acid concentration is measured by measuring the magnitude of the pre-reduction wave current value of the naphthoquinone derivative. The voltammetric acidity measuring apparatus that performs this measurement has a type in which an electrode is immersed in a coexisting electrolyte, and includes a working electrode, a counter electrode, and a reference electrode, or a working electrode and a counter electrode, or a comparative electrode and a working electrode. The sample to be measured is injected into a solution containing a measurement solvent. In addition, although what is disclosed by Unexamined-Japanese-Patent No. 5-264503 is the acidity of a fatty acid, if it is an organic acid, it can measure with this acidity measuring apparatus.
[0005]
[Problems to be solved by the invention]
As described above, when the acid contained in the solution to be measured is measured using the conventional acidity measuring apparatus, it is utilized that the reduction pre-wave current value to be measured is proportional to the acid concentration in the coexisting electrolyte. The acidity is measured. For this reason, even if the acidity of the same solution to be measured is measured, if the mixing ratio of the measurement electrolyte and the solution to be measured is different, the coexisting electrolyte in which they are mixed will have different values of the pre-reduction wave current. As a result, the correct acidity of the solution to be measured cannot be calculated. Therefore, in the past, it was necessary to accurately set the mixing ratio of the measurement electrolyte solution to the solution to be measured and adjust the conditions during measurement. Therefore, when the acidity is measured repeatedly, it is necessary to replace the coexisting electrolyte and to wash each time the acidity is measured.
[0006]
As described above, the measurement using the conventional acidity measuring apparatus takes a lot of time and effort to quantitatively collect and mix each solution, discard the measured coexisting electrolyte, and clean the container for each measurement. Since the solution was replaced, the running cost of the measurement was high.
[0007]
Therefore, an object of the present invention is to provide an acidity measuring device that does not require replacement or washing of the solution for each measurement and can reduce the running cost.
[0008]
Another object of the present invention is to provide an acidity measurement method that does not require replacement or washing of the solution for each measurement.
[0011]
[Means for Solving the Problems]
In order to achieve this object, in the acidity measuring apparatus of the present invention, a calibration curve corresponding to each repeated measurement is stored in the storage unit, and the acidity calculation means selects one from the calibration curve and selects the acidity. Is calculated.
[0012]
Thereby, it is not necessary to replace or wash the solution for each measurement.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The invention described in claim 1 of the present invention performs a first first voltammetric coexistence electrolyte plus the measured solution into the measurement electrolyte proton receptive material containing, detected before reduction置波current The acidity is calculated using the value and the first calibration curve. Further, the second measured solution is added to the coexisting electrolyte after the first measurement, and the second voltammetry is performed. Since the acidity is calculated using the value and the second calibration curve, the voltammetric measurement method is characterized in that the measurement can be repeated twice with the measurement electrolyte solution for one measurement.
[0018]
In the invention described in claim 2 of the present invention, the solution to be measured is further added to the coexisting electrolytic solution after the measurement, and the voltammetry is performed, and the detected pre-reduction wave current value and the calibration curve corresponding to the number of measurements are used. since a voltammetric measurement method of claim 1, wherein repeating the measurement operation of calculating the acidity can be measured further repeated acidity measured batch of measurement electrolyte.
[0019]
According to the third aspect of the present invention, a co-electrolyte having a mixing ratio corresponding to the number of times of measurement is prepared by adding the first solution to be measured to the proton-accepting substance-containing measurement electrolyte, and the first voltammetry. The acidity is calculated using the detected pre-reduction wave current value and the calibration curve, and the second measured solution is added to the coexisting electrolyte after the first measurement, and the second voltammetry is performed. Since it is a voltammetric measurement method characterized in that an approximate value of acidity is calculated using the detected pre-reduction wave current value and the calibration curve, the measurement can be repeated again with the measurement electrolyte solution for one measurement. Since only one line is required, acidity can be easily obtained.
[0020]
In the invention described in claim 4 of the present invention, the solution to be measured is further added to the coexisting electrolyte solution after the measurement, and the voltammetry is performed, and the approximate value of the acidity is calculated using the detected pre-reduction wave current value and the calibration curve. 4. The voltammetric measurement method according to claim 3 , characterized in that the measurement operation is calculated repeatedly, so that the measurement can be repeated with a measurement electrolyte for one measurement, and only one calibration curve is required. Obtainable.
[0021]
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0022]
(Embodiment 1)
First, an acidity measuring apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic external view of an acidity measuring apparatus according to an embodiment of the present invention. In FIG. 1, 1 is an upper cover that covers the measurement unit, 2 is a button for opening the upper cover 1, 3 is an LCD that is a display means for displaying the measured acidity, and 4 is for switching the region depending on the size of the acidity. , 5 is a start / stop button for starting measurement, and 6 is a power button for turning on / off the power of the apparatus.
[0023]
Next, FIG. 2 is a schematic external view in which the upper lid 1 of the acidity measuring apparatus according to the embodiment of the present invention is opened, and FIG. 3 is a control circuit diagram of the acidity measuring apparatus according to the embodiment of the present invention. When the upper lid 1 shown in FIG. 1 is slid, the upper lid 1 is opened as shown in FIG. 2, and a later-described measurement container can be set for measurement in the internal space of the acidity measuring device. Become. This measuring container is configured to be removable from the acidity measuring device main body structurally and electrically.
[0024]
In FIG. 2, 7 is a container for storing a coexisting electrolyte obtained by mixing an orthobenzoquinone derivative, an organic solvent, an electrolyte and a solution to be measured, 8 is a counter electrode, 9 is a working electrode, 10 is a reference electrode, and is called carbon or glassy carbon. The material is glassy carbon or carbon obtained by sintering a plastic foam called PFC at 1000 ° C to 2000 ° C. The measurement container accommodates the coexisting electrolyte in the container 7, and the container cover with the counter electrode 8, the working electrode 9 and the comparison electrode 10 is immersed in the coexisting electrolyte in the container 7 It is what was attached. In addition, it replaces with an ortho benzoquinone derivative, and the same effect mentioned later can be anticipated also with a para benzoquinone derivative.
[0025]
Next, the relation of the coexisting electrolyte stored in the measurement container 7 will be described. The coexisting electrolyte for acidity measurement of this embodiment is a mixture of ethanol and isopropyl alcohol and water at a ratio of 60 wt% ethanol, 20 wt% isopropyl alcohol and 20 wt% water to make 5 mL, and 20 mmol of orthobenzoquinone inducer. In this solution, 150 mmol of sodium chloride is dissolved, and 0.1 mL of the liquid to be measured is mixed with this solvent. It is appropriate to change the ratio of this solvent depending on the kind of acid to be measured, and the above-mentioned solvent is the most suitable solvent for measuring the acidity of fruit juice and the acidity of alcohol. In addition, orthobenzoquinone derivatives and parabenzoquinone inducers are converted into anion radicals by reduction reaction at the electrode and reduced by extracting protons from protic solvents such as alcohol and water (full reduction current flows). In addition, when there is a proton liberated from a fatty acid or an organic acid, it is a proton acceptor that can form a proton adduct, and reduce it to hydroquinone or the like, thereby allowing a pre-reduction wave current proportional to acidity to flow.
[0026]
Reference numeral 11 denotes an installation table on which the measurement container is placed, and a coil for generating a rotating magnetic field is provided inside, and a stirrer 11 is formed together. The stirrer 11 can rotate a stirrer described later after being immersed in a solution in the container 7 by a stirrer driving circuit 27 described later. A stirrer 12 having a magnetic polarity in the coexisting electrolyte is rotatable and rotates in the solution according to the rotating magnetic field by the stirrer 11 so that the coexisting electrolyte can be effectively stirred and stirred. . By stirring according to an instruction from the control unit 15 to be described later, the natural potential that is a potential difference between the working electrode 9 and the comparison electrode 10 can be quickly and stably set. Therefore, quick measurement is possible, and it is not necessary to wait for the start of the second and subsequent measurements more than necessary, and the measurement time can be shortened.
[0027]
Next, a control circuit for controlling the acidity measuring apparatus according to the embodiment of the present invention will be described. FIG. 3 is a control circuit diagram of the acidity measuring device according to one embodiment of the present invention. In FIG. 3, 3 is the above-mentioned LCD display section, 5 ' is a start / stop switch operated by the start / stop button 5, 6' is a power ON-OFF switch that operates when the power button 6 is pressed, and 15 is a microcomputer or the like. 16 is a transmitter, 17 is a frequency divider, 18 is a timer means, 19 is a D / A converter, 20 is an operational amplifier, 21 is a monitoring circuit, 22 is a resistor, 23 is an operational amplifier, 24 Is an A / D converter, 25 is an acidity calculating means, 26 is a storage means, and 27 is a stirrer driving circuit comprising switching elements.
[0028]
When the power button 6 in FIG. 1 is pressed, the LCD 3 becomes operable. Next, when the start / stop button 5 is pressed, the control unit 15 generates a clock internally by the frequency dividing circuit 17 based on the signal generated by the oscillator 9, counts the clock, and the timer 18 starts measuring time. . The timer 18 measures time in units of 1 second. In synchronization with the timer 18, the control unit 15 sends a digital signal (pulse) having a predetermined voltage to the D / A converter 19. The D / A converter 19 converts the digital signal into an analog signal and outputs it to the operational amplifier 20. FIG. 4 is an output diagram from the operational amplifier of the acidity measuring device in one embodiment of the present invention, and FIG. 5 is an output diagram from the integrating circuit of the acidity measuring device in one embodiment of the present invention. As shown in FIG. 4, when time is taken on the horizontal axis and voltage is taken on the vertical axis, the voltage is 5 mV, 10 mV, 15 mV each time the time is counted as 1 second, 2 seconds, 3 seconds,. , ... and will change. The signal output from the operational amplifier 20 is integrated by passing through the RC integration circuit, becomes an analog signal shown in FIG. In the monitoring circuit 21, the operational amplifier constituting the monitoring circuit 21 is used to control the voltage of the counter electrode 8 on the output end side according to the analog signal, and the potential of the comparison electrode 10 on the −input end side becomes the same as the analog signal. Like that. As a result, the potential difference between the comparison electrode 10 and the working electrode 9 falls within a predetermined value range of 0 mV to −1000 mV. On the other hand, the current flowing through the counter electrode 8 is converted into a voltage by passing the voltage across the resistor 22 through the differential amplifier 23, converted from an analog signal to a digital signal via the A / D converter 24, and further controlled. Input to the unit 15. Here, the control unit 15 compares the input current with the voltage swept at a predetermined sweep speed as shown in FIG. 5, thereby giving a pre-peak represented by a dotted line portion in FIG. The standing wave current value is detected. The acidity calculation means 25 calculates the acidity based on the pre-reduction wave current value, and the value is displayed on the LCD 3. The potential of the comparison electrode 10 is also directly input to the A / D converter 24. By switching the input source of the A / D converter 24, the potential of the comparison electrode 10 can be taken into the control unit 15 as a digital signal. . Thus, by calculating the difference from the fixed potential of the working electrode 9, the control unit 15 can monitor the natural potential before measurement, and the natural potential 0 mV to −− which is a measurement start condition for performing highly accurate measurement. Since the next measurement can be started as soon as 5 mV is confirmed, the measurement time can be shortened when performing a plurality of measurements continuously.
[0029]
FIG. 6 is a relational diagram of the reduction current with respect to the voltage sweep of the acidity measuring apparatus according to the embodiment of the present invention. The voltage E is a potential difference between the working electrode 9 and the comparison electrode 10, and the current I flows to the working electrode 8. FIG. 7 is a first relationship diagram between the acidity and the reduction current of the acidity measuring apparatus according to one embodiment of the present invention. In the waveform of FIG. 6, the current value I that gives the pre-reduction wave current value indicated by A and the acidity θ of the acid mixed in the solution to be measured are in a proportional relationship as shown in FIG. In order to convert the measured current value I into acidity, a standard reagent whose acidity is known in advance is prepared, for example, what is the current for acidity 1, 2, 3 and how much the proportionality constant is stored at this time. The means 26 may store and set linear function data (hereinafter referred to as a calibration curve) for calculating acidity indicating the relationship between the current value I and the acidity θ. If the calibration curve is stored in this way, when it is desired to measure an arbitrary acidity, the measured current value I can be converted into the acidity θ by the acidity calculating means 25 constituted by a microcomputer. When the acidity is other than the acidity of the standard reagent, it is desirable to calculate the acidity by complementing the corresponding current value I and the calibration curve.
[0030]
Next, the acidity measuring method in one embodiment of the present invention will be described. FIG. 8 is a second relationship diagram between the acidity and the reduction current of the acidity measuring apparatus according to the embodiment of the present invention. The acidity measurement of the present invention is based on the fact that the calibration curve when the measured solution is added to the coexisting electrolyte after measurement has a predetermined relationship that is uniquely determined from the calibration curve used at the previous measurement. ing. That is, since the liquid to be measured is added again to the measured coexisting electrolyte, the concentration of the contained substance is diluted, and gradually deviates from a predetermined mixing ratio. Therefore, if the content of the operation for measurement is set to a predetermined value, the slope and intercept of the calibration curve are shifted downward at a predetermined rate in the next measurement. The present invention has been made based on such knowledge.
[0031]
Therefore, in the first embodiment, when the measurement is repeated several times, a calibration curve corresponding to the number of times of measurement is stored in the storage means 26 in advance, and a calibration curve corresponding to each measurement is obtained as the acidity calculation means 25. Is selected and read out from the storage means 26, and the acidity is calculated. Thereby, it is possible to measure twice or more by repeatedly using the measurement electrolyte solution for one measurement and changing the calibration curve.
[0032]
Describing in more detail with reference to FIG. 8, it is assumed that the acidity measurement is performed on the solution to be measured for the first measurement having the acidity Q1 and the solution to be measured for the second measurement having the acidity Q2-Q1 in FIG. First, when the coexisting electrolyte solution to which the first solution to be measured is added is voltammetrically obtained, the pre-peak current value IP1 in FIG. 8 is obtained, and since this is the first measurement, the calibration curve stored in the storage means 26 by the acidity calculating means 25. L is selected, the acidity Q1 of the solution to be measured is calculated, and the acidity calculation means 25 automatically counts and stores the number of times this measurement is performed. Next, the solution to be measured in the second measurement is added to the coexisting electrolyte measured in the first time, and the same voltammetry is performed to obtain the pre-peak current value IP2 in FIG. Here, since the acidity obtained by adding the solution to be measured in the second measurement to the solution to be measured in the first measurement is the acidity Q2 in FIG. 3, the pre-peak current value IP2 ′ that can be calculated is obtained by using the calibration curve L. Should be. However, since the solution to be measured for the second measurement is further added to the coexisting electrolyte that has been mixed with the solution to be measured for the first measurement, the pre-peak current value IP2 is changed due to the change in the mixing ratio of the coexisting electrolyte. Will be obtained. Therefore, when the acidity is calculated from the pre-peak current value IP2 using the calibration curve L, an acidity Q2 'different from the correct acidity Q2 is obtained.
[0033]
Here, by taking into account the change in the mixing ratio that causes the acidity calculation error, a calibration curve M corresponding to the mixing ratio for the second measurement is prepared in advance, so that the first peak from the pre-peak current value IP2 is obtained. The acidity Q2 which is a correct value obtained by adding the acidity of the second solution to be measured and the acidity of the second solution to be measured can be obtained.
[0034]
Furthermore, when repeating the measurement after the 3rd time, the several calibration curve corresponding to the frequency | count of a measurement should be similarly prepared previously, and the calibration curve corresponding to each measurement should be selected. Thus, by adding the solution to be measured with the measurement electrolyte for one measurement, a plurality of measurements can be performed.
[0035]
By the way, in the first embodiment described above, a plurality of calibration curves corresponding to the number of measurements are stored in advance in the storage means 26, and the acidity calculation means 25 stores them while counting the number of measurements, and the storage means in the next measurement. 26, a new calibration curve was read out, and the acidity was calculated. However, not all the calibration curve itself is stored in the storage means 26, but what is stored in the storage means 26 is the data constituting the previous calibration curve and the correction coefficient for conversion to the next calibration curve. It may be. In this case, the acidity calculation means 25 reads out the correction coefficient from the counted number of measurements for each number of measurements, calculates and configures a calibration curve in real time at this time, and calculates the acidity using the calculated calibration curve. . Basically the same effect can be expected when all the calibration curves are stored in advance.
[0036]
(Embodiment 2)
The acidity measuring apparatus according to the second embodiment basically has the same configuration as the acidity measuring apparatus according to the first embodiment, but the mixing ratio of the measurement electrolyte solution to the solution to be measured corresponds to the number of times of measurement. Both are mixed in such a ratio that has a high ratio. When the measurement is repeated twice or more for the following reasons, the acidity calculation means 25 calculates the approximate value of the acidity using the only calibration curve stored in the storage means 26. That is, a predetermined amount of the solution to be measured is added to the coexisting electrolyte after the previous measurement and voltammetric, and the approximate value of acidity is calculated using the detected pre-reduction wave current value and the stored calibration curve. A series of measurement operations to be calculated is repeated as many times as necessary.
[0037]
By setting the mixing ratio shown in Embodiment 1 to a sufficiently high mixing ratio with respect to the amount of the solution to be measured, the change in the mixing ratio is reduced even if the solution to be measured is added a plurality of times. The difference between the pre-reduction wave current values IP2 and IP2 ′ of 8 is a value that can be ignored. As a result, it is not necessary to store a plurality of calibration curves as in the first embodiment, and it is not necessary to calculate using a correction coefficient for each number of measurements, and a plurality of calibration curves can be used using only one calibration curve. The acidity to be measured once can be approximately determined. According to the second embodiment, when the acidity is repeatedly measured, an approximate value of the acidity can be easily obtained by the second and subsequent measurements using a single calibration curve. The amount of the measured electrolytic solution may be set to a sufficiently large mixing ratio in consideration of the number of times of measurement with respect to the amount of the solution to be measured. For example, if the mixing ratio is 1% or less, an approximate value with considerable accuracy can be obtained when 3 to 4 measurements are performed. The mixing ratio needs to be increased as the number of repeated measurements is increased.
[0038]
Further, after a predetermined number of measurements, a measurement operation is performed in which the solution to be measured is further added to the coexisting electrolyte and voltammetric, and an approximate value of acidity is calculated using the detected pre-reduction wave current value and the stored calibration curve By repeating the above, it is possible to measure more times with a measurement electrolyte solution for one measurement, and only one calibration curve is required, so that the acidity measuring device can be simplified.
[0039]
【The invention's effect】
As described above, according to the present invention, it is possible to measure the acidity of a solution to be measured multiple times with a measurement electrolyte solution for one measurement with high accuracy, and it is not necessary to replace the measurement solution for each measurement. Running costs can also be reduced. Moreover, the advantageous effect that waste liquids, such as a measurement solution and a washing | cleaning liquid, can also be reduced is acquired.
[0040]
If the measurement electrolyte is mixed at a sufficiently high mixing ratio with respect to the solution to be measured, an approximate value with high acidity accuracy can be obtained by storing only one calibration curve.
[Brief description of the drawings]
FIG. 1 is a schematic external view of an acidity measuring apparatus according to an embodiment of the present invention. FIG. 2 is a schematic external view of an acidity measuring apparatus according to an embodiment of the present invention with an upper lid opened. FIG. 4 is a control circuit diagram of the acidity measuring apparatus according to the embodiment. FIG. 4 is an output diagram from the operational amplifier of the acidity measuring apparatus according to the embodiment of the invention. FIG. 5 is an integrating circuit of the acidity measuring apparatus according to the embodiment of the invention. FIG. 6 is a relationship diagram of the reduction current with respect to the voltage sweep of the acidity measuring device in one embodiment of the present invention. FIG. 7 is a diagram of the acidity and reducing current of the acidity measuring device in one embodiment of the present invention. FIG. 8 is a second relationship diagram between the acidity and the reduction current of the acidity measuring apparatus according to the embodiment of the present invention.
1 Upper lid 2 Open button 3 LCD
4 Range switching button 5 Start / stop button 5 ′ Start / stop switch 6 Power ON / OFF button 6 ′ Power ON / OFF switch 7 Measuring vessel 8 Counter electrode 9 Working electrode 10 Reference electrode 11 Stirrer 12 Stirrer 15 Consists of a microcomputer, etc. Control unit 16 Oscillator 17 Frequency dividing circuit 18 Timer means 19 D / A converter 20 Operational amplifier 21 Monitoring circuit 22 Resistor 23 Differential amplifier 24 A / D converter 25 Acidity calculation means 26 Storage means 27 Stirrer drive circuit

Claims (4)

Perform the first voltammetry of the coexisting electrolyte obtained by adding the solution to be measured to the measurement electrolyte containing the proton-accepting substance, and calculate the acidity using the detected pre-reduction wave current value and the first calibration curve. In addition, the second measured solution is added to the coexisting electrolyte after the first measurement, the second voltammetry is performed, and the acidity is calculated using the detected pre-reduction wave current value and the second calibration curve. A voltammetric measurement method characterized by: It is characterized by repeating the measurement operation of calculating the acidity using a calibration curve corresponding to the detected pre-reduction wave current value and the number of times of measurement by adding the solution to be measured to the coexisting electrolyte after measurement and voltammetrically. The voltammetric measurement method according to claim 1 . The first solution to be measured is added to the measurement electrolyte containing the proton-accepting substance, a coexisting electrolyte having a mixing ratio corresponding to the number of measurements is prepared, and the first voltammetry is performed. The acidity is calculated using a calibration curve, and the second measured solution is added to the coexisting electrolyte after the first measurement, and the second voltammetry is performed. The detected pre-reduction wave current value and the calibration curve A voltammetric measurement method, wherein an approximate value of acidity is calculated using It is characterized by repeating the measurement operation of adding the solution to be measured to the coexisting electrolyte after the measurement and voltammetry, and calculating the approximate value of the acidity using the detected pre-reduction wave current value and the calibration curve The voltammetric measurement method according to claim 3 .

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